Impacts of avian cholera on survival of Common Eiders Somateria mollissima in a Danish colony

Abstract

Capsule The presence of avian cholera depressed annual survival of female Common Eiders in a Danish colony. Aims To estimate the annual survival of adult female Common Eiders in the colony of Helleholm, Denmark, and evaluate the effect of winter temperature and avian cholera on survival. Methods Breeding females were captured and ringed during one-day visits to the colony 1998–2012. Goodness-of-fit was tested using u-care 2.3.2, and annual survival probabilities were estimated in program mark 6.1. We tested for effects of covariates (winter temperature and avian cholera) on survival. Results Goodness-of-fit tests indicated the presence of transient breeders (23%). We estimated a mean survival of 0.884 (95% CI 0.859, 0.905) after the first year. Winter temperature had no significant effect on survival, whereas the effect of avian cholera was significant and accounted for a 14 percentage-point decrease in the annual survival (from 0.922 to 0.781). Conclusion We found a relatively constant survival of female Common Eiders in the colony of Helleholm, at a level consistent with other studies. Years with low adult survival coincided with outbreaks of avian cholera. Hence, epidemic disease, rather than winter temperature, seemed to negatively affect the adult female survival in the study colony.